Research partner ECN used the cell mechanically stacked on a 6 in2 silicon bottom cell with its proprietary MWT-SHJ (metal-wrap-through silicon heterojunction) design to reach an efficiency of 26.3% efficiency is achieved, an increase of 3.6 percentage points over the efficiency of other versions and challenging the efficiency of silicon.
“By optimising the ITO (indium tin oxide) composition and deposition conditions as well as careful design of the anti-reflection coating (ARC), an extremely high transparency is achieved for the top electrode, despite the low temperature process window,” said Dong Zhang, researcher at Solliance. Using this ITO, with a sheet resistance as low as 40 Ohm per square, a perovskite photovoltaic cell was made with an average transmittance in the relevant near infrared wavelength range (800 – 1200 nm) of 93 %. This is significantly higher than the state of the art, which is below 85 %.
“The active area of the tested small semi-transparent perovskite cell is 0.09 cm2 while the power conversion efficiency is 16.4 %. Solliance employs different technologies in development to ensure the celll can move to volume production. “Now that the device was proven with spin coated layers, we use pilot scale equipment provided by our industrial partners to scale it to a viable industrial production process,” said Sjoerd Veenstra, program manager Perovskite Solar Cells at Solliance. “Also the expertise of industrial partners of Solliance in sheet-to-sheet spatial ALD and laser interconnection of thin film cells is used to scale-up the technology to 30×30 cm2 demonstration modules.”
The MWT-SHJ c-Si top cell was processed by Choshu Industry in collaboration with ECN and the perovskite bottom cell contributes 9.9 percentage points to the tandem cell efficiency. This shows how feasible it is to achieve significant efficiency gain even over high-end crystalline silicon technology and based on industrial process technology. ECN, soon to merge with TNO, is working to further optimise the bottom cells and the module integration to obtain higher conversion efficiency, reliability, and lower production cost.
Solliance is a partnership of R&D organizations from the Netherlands, Belgium and Germany working in thin film photovoltaic solar energy, coordinating the activities of 250 researchers in industry, at research institutes and universities including ECN, imec, TNO, Holst Centre, Forschungszentrum Jülich, University Hasselt, University of Twente, Delft University of Technology and Eindhoven University of Technology.
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